Recently passed laws and regulations, e.g. the Clean Air Act, have placed strict requirements on the amount of mercury that can be emitted into the atmosphere from the boilers of coal-fired electric power generation plants, as well as other industrial plants. Thus, power generation companies have invested millions of dollars in developing new technologies for capturing mercury in the flue gases emitted from power plants. One such technology involves injecting finely ground Powdered Activated Carbon (“PAC”) into the flue gas stream. The PAC is a sorbent and can adsorb and absorb a majority of mercury that would otherwise be exhausted into the atmosphere. After the PAC is injected into the flue gas, the flue gas is passed through a baghouse that serves as a large filter to remove the PAC, thus removing the mercury.
Conventional PAC injection systems include a silo, a feeder, an educator, and a blower. PAC is stored in the silo and fed to the educator by the feeder. The educator is powered by the blower, which creates an air stream forcing the PAC through the educator and a piping system, and ultimately into the flue gas stream. Unfortunately, conventional systems employing a blower and educator have many disadvantages, a few of which will be explained. First, the blower and educator are expensive components to install. Second, because the blower must create a powerful air stream to force PAC through the system, from the educator to the flue gas, the blower continually causes damage to the piping system. Thus, under normal circumstances, the piping system must be replaced every two-to-six weeks, which leads to further expenses in materials and labor. Third, because the piping system from a blower must be replaced so frequently, many power plants employ as many as three conventional PAC injection systems per boiler system to ensure that PAC in continuously injected even if one system is down under repair. Fourth, depending on the size of the boiler system, conventional PAC injection systems may require PAC injection rates exceeding 400 pounds per hour, thus creating a need for large silos to store such large amounts of PAC. Because many boiler systems run 24 hours a day, 365 days a year, the cost associated with PAC, not to mention the materials and labor to repair the damaged PAC injection systems, can be tremendous.
Therefore, there is a desire for improved systems and methods for injecting PAC into the flue gas of a boiler system. Specifically, there is a desire for systems and methods for injecting PAC into the flue gas of a boiler system that limits damage to the piping systems and that is capable of decreasing the PAC injection rates (over conventional systems) while maintaining sufficient mercury removal.